scholarly journals Limits on long-timescale radio transients at 150 MHz using the TGSS ADR1 and LoTSS DR2 catalogues

2021 ◽  
Author(s):  
Iris de Ruiter ◽  
Guillaume Leseigneur ◽  
Antonia Rowlinson ◽  
Ralph A M J Wijers ◽  
Alexander Drabent ◽  
...  
Keyword(s):  
Flux Density ◽  
Radio Sources ◽  
Compactness Criterion ◽  
Compact Source ◽  
Upper Limit ◽  
Sky Survey ◽  
Data Release ◽  
Transient Sources ◽  
Radio Transients ◽  
Compact Sources

Abstract We present a search for transient radio sources on timescales of 2-9 years at 150 MHz. This search is conducted by comparing the first Alternative Data Release of the TIFR GMRT Sky Survey (TGSS ADR1) and the second data release of the LOFAR Two-metre Sky Survey (LoTSS DR2). The overlapping survey area covers 5570 $\rm {deg}^2$ on the sky, or 14 per cent of the total sky. We introduce a method to compare the source catalogues that involves a pair match of sources, a flux density cutoff to meet the survey completeness limit and a newly developed compactness criterion. This method is used to identify both transient candidates in the TGSS source catalogue that have no counterpart in the LoTSS catalogue and transient candidates in LoTSS without a counterpart in TGSS. We find that imaging artefacts and uncertainties and variations in the flux density scales complicate the transient search. Our method to search for transients by comparing two different surveys, while taking into account imaging artefacts around bright sources and misaligned flux scales between surveys, is universally applicable to future radio transient searches. No transient sources were identified, but we are able to place an upper limit on the transient surface density of <5.4 · 10−4 deg−2 at 150 MHz for compact sources with an integrated flux density over 100 mJy. Here we define a transient as a compact source with flux density greater than 100 mJy that appears in the catalogue of one survey without a counterpart in the other survey.

scholarly journals The Molonglo Deep Sky Survey of Radio Sources. II. Declination Zone -62°

1977 ◽  
Vol 30 (2) ◽  
pp. 231 ◽  
Author(s):  
JG Robertson
Keyword(s):  
Flux Density ◽  
Lower Limit ◽  
Solid Angle ◽  
Radio Sources ◽  
Upper Limit ◽  
Sky Survey ◽  
Deep Survey ◽  
The Right

Results are given for the second zone of a deep survey made at 408 MHz with the Molonglo cross. The catalogue lists positions and flux densities for 95 sources, none of which has been previously catalogued, in a solid angle of 5�51 x 10-3 sr. The right ascensions covered (with some excluded areas) are 18h 26m-OOh 06m, with a range in declination of 45'. The lower limit of flux density is 84 inJy. An upper limit of 1000 mJy has also been imposed. The position uncertainties are typically 12''at 100 mJy and 6# at 250 mJy.

scholarly journals The Molonglo Deep Sky Survey of Radio Sources. I. Declination Zone -20°

1977 ◽  
Vol 30 (2) ◽  
pp. 209 ◽  
Author(s):  
JG Robertson
Keyword(s):  
Error Analysis ◽  
Flux Density ◽  
Lower Limit ◽  
Solid Angle ◽  
Radio Sources ◽  
Contour Maps ◽  
Upper Limit ◽  
Sky Survey ◽  
Deep Survey

Results of a deep survey made at 408 MHz with the Molonglo cross are given. The catalogue lists positions and flux densities for a total of 373 radio sources, most of which have not previously been catalogued, in a solid angle of 0�0201 Sf. This covers (with some excluded areas) right ascensions 0l h oom-06h 44m and 13h 45m-17h 19m, with a range in declination of 41'. Eighteen contour maps are given of sources that are extended or have very close companions. A thorough error analysis is given, as well as new operational definitions of completeness and reliability. The lower limit of flux density is 88 mJy, which is five times the r.m.s. error. An upper limit of 1000 mJy has also been imposed. Typical errors in positions are 15" at 100 mJy and 6" at 250 mJy.

scholarly journals VLBI Survey of a Complete Sample of Active Nuclei and Quasars

1984 ◽  
Vol 110 ◽  
pp. 15-24 ◽  
Author(s):  
T. J. Pearson ◽  
A.C.S. Readhead
Keyword(s):  
Flux Density ◽  
Radio Sources ◽  
Complete Sample ◽  
Limited Sample ◽  
Extragalactic Radio Sources ◽  
5 Ghz ◽  
Number Of Classes ◽  
Compact Sources ◽  
Continuous Range

We have conducted a VLBI survey of a complete, flux-density limited sample of 65 extragalactic radio sources, selected at 5 GHz. We have made hybrid maps at 5 GHz of all of the sources accessible to the Mark-II system. The sources can be divided provisionally into a number of classes with different properties: central components of extended double sources, steep-spectrum compact sources, very compact (almost unresolved) sources, asymmetric sources (sometimes called “core-jet” sources), and “compact double” sources. It is not yet clear whether any of these classes is physically distinct from the others, or whether there is a continuous range of properties.

scholarly journals A VO study of SDSS AGNs with X-ray emission from ROSAT-PSPC pointed observations

2006 ◽  
Vol 2 (14) ◽  
pp. 581-581
Author(s):  
Robert J. Hanisch ◽  
Anatoly A. Suchkov ◽  
Timothy M. Heckman ◽  
Wolfgang H. Voges
Keyword(s):  
Survey Data ◽  
Sloan Digital Sky Survey ◽  
Radio Sources ◽  
X Ray ◽  
Sky Survey ◽  
Data Release

We use VO facilities to study AGNs with X-ray emission. We present a sample of 1744 of Type 1 AGNs from the Sloan Digital Sky Survey Data Release 4 (SDSS DR4) spectroscopic catalog with X-ray counterparts in the White-Giommi-Angelini catalogue (WGACAT) of ROSAT-pspc pointed observations. Of 1744 X-ray sources, 1410 (80.9%) are new AGN identifications. Of 4,574 SDSS DR4 AGNs for which we found radio matches in the catalogue of radio sources from the Faint Images of the Radio Sky at Twenty (FIRST) cm survey, 224 turned up in our sample of SDSS X-ray AGN.

scholarly journals Compact Source Detection in Multichannel Microwave Surveys: From SZ Clusters to Polarized Sources

2012 ◽  
Vol 2012 ◽  
pp. 1-14 ◽  
Author(s):  
Diego Herranz ◽  
Francisco Argüeso ◽  
Pedro Carvalho
Keyword(s):  
State Of The Art ◽  
A Priori ◽  
Radio Sources ◽  
Source Detection ◽  
A Priori Information ◽  
Compact Source ◽  
Detection Techniques ◽  
Spectral Behaviour ◽  
Priori Information ◽  
Compact Sources

We describe the state-of-the art status of multifrequency detection techniques for compact sources in microwave astronomy. From the simplest cases where the spectral behaviour is well known (i.e., thermal SZ clusters) to the more complex cases where there is little a priori information (i.e., polarized radio sources) we will review the main advances and the most recent results in the detection problem.

scholarly journals The Murchison Widefield Array Commissioning Survey: A Low-Frequency Catalogue of 14 110 Compact Radio Sources over 6 100 Square Degrees

2014 ◽  
Vol 31 ◽  
Author(s):  
Natasha Hurley-Walker ◽  
John Morgan ◽  
Randall B. Wayth ◽  
Paul J. Hancock ◽  
Martin E. Bell ◽  
...  
Keyword(s):  
Flux Density ◽  
Noise Level ◽  
Angular Resolution ◽  
Low Frequency ◽  
Radio Sources ◽  
Reduction Strategy ◽  
Sky Survey ◽  
Field Boundaries ◽  
Murchison Widefield Array ◽  
Finding Method

AbstractWe present the results of an approximately 6 100 deg2 104–196 MHz radio sky survey performed with the Murchison Widefield Array during instrument commissioning between 2012 September and 2012 December: the MWACS. The data were taken as meridian drift scans with two different 32-antenna sub-arrays that were available during the commissioning period. The survey covers approximately 20.5 h < RA < 8.5 h, − 58° < Dec < −14°over three frequency bands centred on 119, 150 and 180 MHz, with image resolutions of 6–3 arcmin. The catalogue has 3 arcmin angular resolution and a typical noise level of 40 mJy beam− 1, with reduced sensitivity near the field boundaries and bright sources. We describe the data reduction strategy, based upon mosaicked snapshots, flux density calibration, and source-finding method. We present a catalogue of flux density and spectral index measurements for 14 110 sources, extracted from the mosaic, 1 247 of which are sub-components of complexes of sources.

scholarly journals One- and two-point source statistics from the LOFAR Two-metre Sky Survey first data release

2020 ◽  
Vol 643 ◽  
pp. A100
Author(s):  
T. M. Siewert ◽  
C. Hale ◽  
N. Bhardwaj ◽  
M. Biermann ◽  
D. J. Bacon ◽  
...  
Keyword(s):  
Point Source ◽  
Flux Density ◽  
Large Scale ◽  
Value Added ◽  
Radio Sources ◽  
Sky Survey ◽  
Point Correlation ◽  
Point Correlation Function ◽  
The Universe ◽  
Density Threshold

Context. The LOFAR Two-metre Sky Survey (LoTSS) will eventually map the complete Northern sky and provide an excellent opportunity to study the distribution and evolution of the large-scale structure of the Universe. Aims. We test the quality of LoTSS observations through a statistical comparison of the LoTSS first data release (DR1) catalogues to expectations from the established cosmological model of a statistically isotropic and homogeneous Universe. Methods. We study the point-source completeness and define several quality cuts, in order to determine the count-in-cell statistics and differential source count statistics, and measure the angular two-point correlation function. We use the photometric redshift estimates, which are available for about half of the LoTSS-DR1 radio sources, to compare the clustering throughout the history of the Universe. Results. For the masked LoTSS-DR1 value-added source catalogue, we find a point-source completeness of 99% above flux densities of 0.8 mJy. The counts-in-cell statistic reveals that the distribution of radio sources cannot be described by a spatial Poisson process. Instead, a good fit is provided by a compound Poisson distribution. The differential source counts are in good agreement with previous findings in deep fields at low radio frequencies and with simulated catalogues from the SKA Design Study and the Tiered Radio Extragalactic Continuum Simulation. Restricting the value added source catalogue to low-noise regions and applying a flux density threshold of 2 mJy provides our most reliable estimate of the angular two-point correlation. Based on the distribution of photometric redshifts and the Planck 2018 best-fit cosmological model, the theoretically predicted angular two-point correlation between 0.1 deg and 6 deg agrees reasonably well with the measured clustering for the sub-sample of radio sources with redshift information. Conclusions. The deviation from a Poissonian distribution might be a consequence of the multi-component nature of a large number of resolved radio sources and/or of uncertainties on the flux density calibration. The angular two-point correlation function is < 10−2 at angular scales > 1 deg and up to the largest scales probed. At a 2 mJy flux density threshold and at a pivot angle of 1 deg, we find a clustering amplitude of A = (5.1 ± 0.6) × 10−3 with a slope parameter of γ = 0.74 ± 0.16. For smaller flux density thresholds, systematic issues are identified, which are most likely related to the flux density calibration of the individual pointings. We conclude that we find agreement with the expectation of large-scale statistical isotropy of the radio sky at the per cent level. The angular two-point correlation agrees well with the expectation of the cosmological standard model.

scholarly journals Optical Properties of FRI Radio Galaxies

1996 ◽  
Vol 175 ◽  
pp. 238-239
Author(s):  
Michael J. Ledlow ◽  
Frazer N. Owen
Keyword(s):  
Optical Properties ◽  
Flux Density ◽  
Radio Galaxies ◽  
Cluster Center ◽  
Radio Sources ◽  
Complete Sample ◽  
Abell Clusters ◽  
Ccd Observations ◽  
Twin Jets ◽  
Compact Sources

From the VLA 20cm survey of ≃ 500 Abell clusters reported by (Ledlow and Owen, 1995), we have obtained optical R-Band CCD observations and optical spectra for 265 radio galaxies. The survey is complete for 20cm flux density greater than 10 mJy within 0.3 corrected Abell radii of the cluster center. All Abell clusters with measured z < 0.09 were surveyed. This statistically complete sample was supplemented by ≃ 200 clusters with 0.09 < z < 0.25 including sources with flux density > 200 mJy. Only 6% of the sample consists of FR II radio sources, the remainder are twin-jets, tailed, or compact sources associated with the FR I class.

scholarly journals The Planck Compact Source Catalogues: present and future

2015 ◽  
Vol 11 (A29B) ◽  
pp. 61-61
Author(s):  
Marcos López-Caniego ◽  
Keyword(s):  
Flux Density ◽  
Spectral Energy Distribution ◽  
Single Frequency ◽  
Spectral Energy ◽  
Compact Source ◽  
Frequency Detection ◽  
Frequency Coverage ◽  
The Impact ◽  
Compact Sources ◽  
Large Frequency

AbstractThe Planck Collaboration has produced catalogues of radio and sub-millimeter compact sources at the nine Planck frequencies in total intensity and polarization. In particular, the 2015 Second Planck Catalogue of Compact Sources (PCCS2) contains over 45.000 sources detected in the Planck full mission maps. Since the Planck instruments have polarization capabilities in seven of its nine detectors, we were able to measure the polarized flux density of over 600 sources between 30 and 353 GHz. But we are searching not only for compact sources in single frequency maps, and we take advantage of the large frequency coverage of Planck to search for objects with specific emission laws. This is the case of the SZ catalogue of cluster of galaxies (PSZ2), that lists 1653 clusters, 1203 of which are confirmed clusters with clear associations in external data-sets, and the Galactic cold clump catalogue (PGCC) with 13188 objects. The Planck Collaboration has also published a list of high-redshift source candidates (see the report by Ludovic Montier here). These objects are rare bright sub-millimeter sources with an spectral energy distribution peaking between 353 and 857 GHz, and have been detected combining Planck and IRAS data. The colours of most of these objects are consistent with redshifts z>2, a fraction of which could be lensed objects with redshifts between 2 and 4.But new catalogues are foreseen. A multi-frequency compact source catalogue is being produced selecting sources at radio frequencies and studying them across all Planck bands. Multi-frequency catalogues can be difficult to produce in experiments like Planck that have a large frequency coverage and very different resolutions across bands. In some cases, a source can be very bright across the whole Planck frequency range and it is easy to do the associations across channels. However, it frequent to find unrelated sub-millimeter sources within the half-degree beam of the 30 GHz low frequency detector, and the association work must be done with great care. For this purpose, we are combining a multi-frequency detection procedure with a principal component analysis to produce the catalogue. In addition, for those sources where a clear identification can be made, we will attempt to include flux density information from Herschel and other experiments, in particular for those blazars that are bright in radio, sub-mm and even in gamma-ray frequencies, as seen by Fermi. Moreover, Planck has made available to the community the single survey frequency maps that allow astronomers to study the long-term variability of their favourite sources. New functionalities will be also added to the Planck Legacy Archive†, for example a timeline-cutting tool that will allow one to produce full-sky maps from the Planck timelines for specific periods of time allowing for short-term variability studies of compact sources (e.g., flares). The unique frequency coverage of Planck make these catalogues very valuable for other experiments using the Planck compact source catalogues. For example, experiments like QUIJOTE use Planck selected sources to study the impact of polarized radio source emission on their cosmological fields and other CMB experiments will use Planck polarized compact source information for calibration.

Sign in / Sign up

Export Citation Format

Share Document